This invention pertains to manifolds for internal combustion engines and more specifically to stamped manifolds for small internal combustion engines.
With the development of the vertical and horizontal shaft overhead valve type of engine, the exhaust port in the cylinder head is oriented so that, in certain applications, an exhaust manifold is required between the muffler and the cylinder head exhaust port. In such applications the manifold, besides providing a conduit between the exhaust port and the muffler, changes the direction of flow of the exhaust gas. Certain surfaces of the exhaust muffler are therefore exposed to direct impingement of the hot exhaust gases which exit from the engine exhaust port. Such manifolds must therefore be able to withstand the high temperatures of the exhaust gas, which temperatures may be in the range of 1,100.degree. F. to 1,300.degree. F.
The majority of exhaust manifolds used on prior art small single cylinder engines have been manufactured from cast iron. Such manifolds, after casting, must be machined to accomodate the exhaust port mounting bolts for securing the manifolds to the engine and to the muffler. Such manifolds are therefore relatively expensive both because of the cost of materials and the cost of machining the manifolds. Furthermore, such cast manifolds are relatively heavy and bulky requiring more space than a stamped manifold and therefore add undesired weight to the engine which is especially undesirable in small engines.
In some prior art engines stamped exhaust manifolds have been used. However, such stamped exhaust manifolds have been manufactured from stainless steel or other exotic high temperature resistant metals since cold rolled draw quality steel would not be resistant to the high temperatures encountered in such manifolds. While such stainless steel stamped manifolds are resistant to flame burn-through, such manifolds are also relatively expensive because of the cost of the metals involved and are furthermore difficult to manufacture because stainless steel tends to work harden in deep draw stamping operations. The stamping process therefore requires annealing steps between drawing operations thus adding further manufacturing cost. Lastly, the welding process for welding the several parts of such stainless steel manifolds together is a difficult and expensive operation.
It is therefore desired to provide a stamped exhaust manifold for an internal combustion engine which may be manufactured from relatively inexpensive draw quality sheet metal which can be formed into an effective, inexpensive manifold which is not subject to flame burn-through.